Cross-linked graft copolymer of styrene and methyl methacrylate upon a butadiene polymer

ABSTRACT

Butadiene-styrene-methyl methacrylate copolymers prepared by graft-polymerization with cross-linked butadiene or polybutadiene-styrene copolymer latex of styrene-methyl methacrylate monomers and a cross-linking agent capable of copolymerizing with said monomers in two steps. Polyvinyl chloride resins incorporated with the graft copolymer exhibits improved mechanical strength and other physical properties.

United States Patent Amagi et al.

[ 1 June 20, 1972 [54] CROSS-LINKED GRAFT COPOLYMER OF STYRENE AND METHYL METHACRYLATE UPON A BUTADIENE POLYMER [72] Inventors: Yasuo Amagi; Masaki Ohya; Zenya Shllki;

I-laruhiko Yusa, all of lwaki-shi, Japan Kureha Kagaku Kogyo Kabushiki Kaisha, Tokyo, Japan [22] Filed: Nov. 14, 1969 [2|] Appl.N0.: 876,920

[73] Assignee:

Related US. Application Data [63] Continuation-impart of Ser. No. 570,261, Aug. 4,

1966, abandoned.

[30] Foreign Application Priority Data 7 Aug. 9, 1965 Japan ..40/48036 Feb. 5, 1966 Japan... ..4l/6652 Feb. 5, 1966 Japan ..4l/6653 [5 2] US. Cl. .260/880 R, 260/29.7 UA, 260/29.7 UP, 260/876 R, 260/885, 260/886 [5i Int. Cl ..C08f 19/08, C08f 37/l8 Primary Emminer-Murray Tillman Assistant Examiner-Wilbert .l. Briggs, Sr. Attorney-Wenderoth, Lind & Ponack [57] ABSTRACT Butadiene-styrene-methyl methacrylate copolymers prepared by graft-polymerization with cross-linked butadiene or polybutadiene-styrene copolymer latex of styrene-methyl methacrylate monomers and a cross-linking agent capable of copolymerizing with said monomers in two steps.

Polyvinyl chloride resins incorporated with the graft copolymer exhibits improved mechanical strength and other physical properties.

2 Claims, 1 Drawing Figure PATENTEDmzo I972 3,671,610

INVENTOR M 6 Z/M REFERENCE TO RELATED APPLICATION This application is a continuation-in-part of our copending application, Ser. No. 570,261 filed Aug. 4, l966,and now abandoned, for Polymer Composition and Process for Producing the Same.

BACKGROUND OF INVENTION This invention relates to butadiene-styrene-methyl methacrylate graft copolymers (hereinafter referred to as MBS resins"). More particularly, the invention concerns a new MBS resin which, upon being mixed with a polyvinyl chloride or a copolymer containing a polyvinyl chloride as a principal constituent, is capable of imparting high transparency, impact resistance, and resistance to the stress whitening through bending to the resulting shaped articles of the composition.

Heretofore, the so-called graft copolymers" produced by causing a post polymerization (or a consecutive polymerization which will hereinafter be denoted merely as polymerization") of vinyl monomers such as styrene, acrylonitrile, or methyl methacrylate either independently or as a mixture of a plurality thereof to a rubber-like polymer latex have been .well 7 known.

These graft copolymers have good mechanical strength and have, therefore, been used independently for various shaped articles. In addition, these graft copolymers have been mixed with other resins such as polyvinyl chlorides to improve the impact resistance of shaped articles of these other resins.

However, most of the graft copolymers produced by hitherto known methods, while being capable of improving theimpact resistance of polyvinyl chlorides when mixed and kneaded therewith, have been disadvantageous in that they produce products which are deficient in transparency and lack in resistance to the weathering. Particularly, resin compositions containing acrylonitrile as a' constituent thereof has disadvantages such as low heat stability.

Furthermore, when shaped articles produced from these resins such as sheets, bottles, etc. are bent, the-bent portions of the articles as well as the neighboring portions thereof become extremely cloudy, whereby only products of low commercial value are obtained.

, SUMMARY OF INVENTION It is therefore an object of the present invention to provide MBS resins which, upon being mixed and kneaded in minimal quantities with polyvinyl chloride, is capable of imparting to shaped articles formed from the resulting resin composition practically excellent propeties such as high impact resistance, high transparency, resistance to weather, high heat stability, and almost no occurrence of the stress-whitening at bent portions of the products.

It is another object of the present invention to provide polyvinyl chloride resin composition produced by mixing and kneading polyvinyl chloride and the above-mentioned MBS resins manufactured for the above-mentioned particular purpose and exhibiting practically high impact resistance, high transparency, resistance to weather, high heat stability, and almost no occurrence of the stress-whitening at bent portions of products formed from such resin composition.

It is other object of the present invention to provide an improved method of producing cross-linked graft copolymer of butadiene-styrene-methylmethacrylate-divinyl compound having excellent properties in a relatively simple and economical manner.

The foregoing objects and other objects of the present invention will become more apparent from the following description of the invention when read in conjunction with the accompanying drawing.

BRIEF DESCRIPTION OF DRAWING In the drawing, single FIGURE is a graphical representation with triangular co-ordinates indicating the proportions of three constituent monomers of MBS resins according to the invention.

DETAILED DESCRIPTION OF INVENTION The MBS resins of the invention can be obtained, in general, by emulsion-polymerization of butadiene or a monomer mixture of butadiene as the principal constituent and styrene, with addition of a small quantity of a cross-linking agent, to produce a polymer latex, causing a monomer mixture containing styrene and methyl methacrylate and a small quantity of a cross-linking agent as an additive to be adsorbed on the polymer latex and be polymerized thereon, or further adding thereto methyl methacrylate containing a cross-linking agent, and causing polymerization, and subjecting the latex thus obtained to salting out, whereby MBS resin in the form of fine particles can be obtained.

By mixing from 5 to 20 parts by weight of anMBS resin obtained in this manner with from-95 to parts by weight of a described excellent properties.

This MBS resin according to the invention may be considered to function in the following manner. When this MBS resin is mixed and'kneaded with a polyvinyl chloride, rubber component particles of constant size are'dispersed within the polyvinyl chloride in a form wherein they are protected by respective layers therearound of styrene-methyl methacrylate resin and methyl methacrylate resin. In this case, the styrenemethyl methacrylate layer is highly compatible with the rubber component, while the methyl methacrylate layer is highly compatible with the polyvinyl chloride. Moreover, as the plastic constituents in therespective latex particles thus graft-copolymerized are all cross-linked, the adhesion between the MBS particles is weak, whereby these particles can be readily dispersed within the polyvinyl chloride resin in a uniform manner. As a result, the transparency of the product is increased, and, at the same time, separation of the rubberplastic phase and the polyvinyl chloride phase does not occur even at the time of bending the shaped articles, whereby stress-whitening also does not occur. The impact-resistance of polyvinyl chloride composition has heretofore been measured in accordance with ASTM D-256-56 (Izod or Charpy impact strength values). However, as described at pages 199 to 206 of Modern Plastics, June, 1956, the Izod impact strength test is to subject a notched test sample to destruction, hence the result will eventually be different from the actualstreng'th of the shaped articles.

An important feature of the present invention is that the MBS resins obtained thereby are uniformly dispersed in solvents such as benzene, toluene, and tetralin and that the solution specific viscosity v,,,/c (4 grams/liter, in benzene) thereof is within the range of from 0.01 to 0.06. The solution viscosity of an MBS resin obtained according to the invention decreases with increase in the degree of cross-linking and increase with decrease in the degree of cross-linking.

We have found that, while the shaped articles obtained by mixing and kneading of an MBS graft copolymer having a value of v,,,/c lower than 0.01 anda polyvinyl chloride possess These MBS resins and ABS resins have a further disadvantage in that shaped articles produced by kneaded mixtures of these resins with polyvinyl chlorides do not have very good transparency.

Through consideration of these disadvantageous features of these resins obtained by known methods, we have discovered that there exists a close interrelationship between the solution viscosity and transparency as well as the stress-whitening of MBS resins, as described more fully hereinafter.

A further feature of the present invention is that the index of refraction of the MBS graft copolymer produced thereby are within the range of from L528 to 1.540. That is, the indexes of refraction of polyvinyl chlorides and copolymers with vinyl chloride as their principal constituents are from 1.530 to 1.538 at 20 C., and it is important that the indexes of refraction of the MBS resins to be admixed therewith coincide almost exactly with these values. If the index of refraction is outside of the above-stated range, the resulting shaped article will become non-transparent or in some cases produce scattered light of strong purple color.

The indexes of refraction n at 20 C. of polymersof butadiene, methyl methacrylate, and styrene are 1.515, 1.494, and 1.590, respectively, and in the case of the polymers according to the invention, it may be considered that the additive property (or additivity rule) due to the weight composition is approximately realized.

As shown in the graphical representation of the accompanying drawing, when the entire composition of a resin is contained within the region bounded by the reference letters ABCDEF, and, at the same time, the resin possesses a value of v,,,/c within the above specified range, mixing and kneading of the resin with a polyvinyl chloride produces a transparent shaped article.

More specifically, it is requisite that the composition of the three monomersbe from. 24 to 60 percent of butadiene, from 22 to 43 percent of styrene, and from-5 to 46 percent of methyl methacrylate.

A further important feature of the MBS resins according to the invention is the compositional ratio of the rubber constituent and the plastics constituent. Of course, if only impact resistance were to be considered as a problem, as large a rubber content as possible would be desirable, but if the rubber content is increased to an extreme degree, agglomeration or lumping will result from steps such as salting out and drying, or the mixing and kneading with the polyvinyl chloride will, be made difficult, and as a result uniform dispersion cannot be attained On the other hand, in the case where the rubber content is below 40 weight percent, the effect of imparting impact resistance is small, and the other physical properties of polyvinyl chloride such as heat and temperature resistance and gas impermeability become deficient. That is, the compositional ratio by weight of the rubber constituent and the plastics constituent is preferably in the range of (40 to 75) parts by weight of rubber: to 25) parts by weight of plastics.

For the rubber constituent, a butadiene polymer or a butadiene styrene copolymer which has or has not been crosslinked is used. It has been found that in the case of a butadiene styrene copolymer, a styrene content of 40 weight percent or less produces excellent results.

For the plastics constituent, a polymer produced by causing a monomer mixture of styrene and methyl methacrylate containing a cross-linking agent to be adsorbed and polymerized on rubber latex particles is used. It has been found that the styrene content in the monomer mixture is preferably in the range of from 40 to 80 weight percent.

In this case, it has been found that, rather than the plastics constituent of a specific quantity be polymerized in one step on the rubber constituent, it is preferable to resort to a twostep graft-polymerization process in which the plastics constituent is divided into two parts, and which comprises carrying out a first-graft-polymerization step, adding a monomer mixture of styrene and a part of methyl methacrylate containing a cross-linking agent upon completion of the greater part of the first graft-polymerization step, and subsequently carrying out a second graft-polymerization step by adding the remainder portion of methyl methacrylate.

This two-step method has the effect of further improving the properties of the blending of the MBS resin produced with the polyvinyl chloride and increasing the rate of dispersion into the polyvinyl chloride. Furthermore, compatibility of the MBS resins and the polyvinyl chloride increases and the stresswhitening through bending is improved.

The quantity of MMA monomer polymerized in the second step is preferably from 10 to percent byweight to the total methyl methacrylate. Furthermore, even in the case where the graft-polymerization of the plastics constituent with respect to the rubber constituent is carried out in two steps, the crosslinking agent should be added in both the first and second steps.

The cross-linking agent to be added to the rubber component or graft component according to .the invention is selected from among those which copolymerize well with styrene, butadiene, and methyl methacrylate. Examples of suitable cross-linking agents are divinyl benzene and dimethacrylates such as mono-, di-, tri-, or tetra-ethylene glycol dimethacrylate and l, 3-butylene glycol dimethacrylate. The quantity ofthe cross-linking agent used is from 0.0l to 5 weight percent of the total quantity of the monomers which exist in the copolymers.

The polyvinyl chlorides suitable for use according to the invention are those obtainable by various known methods such as emulsion-polymerization and suspension-polymerization. in addition to independent polymers, it is also possible to use a copolymer consisting of 70 percent or more of vinyl chloride and other monomers to be copolymerized therewith such as mono-olefin monomers, e.g., vinyl acetate, acrylonitrile, vinylidene chloride, alkyl vinyl ether, etc. or mixtures thereof. From 5 to 20 parts by weight of a resin obtained according to the invention is mixed with from to 80 percent by weight of a polyvinyl chloride of the above stated character.

While it is possible to carry out the mixing, in general, with the materials in powder form by means of apparatus such as a roll mill or a Bumbury type mixer, it is also possible to mix the latex obtained and the polyvinyl chloride ,latexand then to subject the resulting mixture to salting out or spray drying thereby to produce a mixed resin composition.

As described above, the MBSjresins according to the invention, when mixed with polyvinyl chlorides, impart excellenttransparency and impact resistance to the shaped articles formed from the resulting mixture resins. The use of these MBS resins, however, is not limited to only that for mixing with polyvinyl chlorides, these MBS resins being useful also for mixing with other resins as, for example, chlorinated polyvinyl chloride and vinylidene chloride copolymers thereby to increase their impact-resistant strength.

PREFERRED EMBODIMENTS In order to indicate still more fully the nature and utility of the present invention, the following examples of practice thereof are set forth, it being understood that these examples are presented as being illustrative only, and that they are not intended to limit the scope of the invention.

EXAMPLE 1 charged were then caused to react at 40 C. for approximately l7 hours, at which time no further pressure drop was observable.

Next, to the resulting charge, a monomer mixture of 300 grams of styrene containing 0.5 gram of CHP and 3 grams of Fifty of these bottles were cooled to 5 C., filled with water, and subjected to repeated free drop tests from a height of 1 meter until breakage occurred. As a result, the average number of drops for breakage was 29 drops. For comparison,

notched test piece according to ASTM D-256-56 was 85 kg.cm./cm. The light transmittance of the sheet according to ASTM D-l003-52 was 8L5 percent, and the haze value was 3.5 percent. Furthermore, when a sheet of 1 mm. thickness of the same resin was bent through 180 C. at 25 C., clouding was observed to be extremely less.

In addition, when a mixture of 0.1 part of calcium stearate, 0.36 part of zinc stearate, and 6 parts of an epoxy compound of soybean oil was used in place of the above described stabilizing agent, and bottles, each of 530 cc. capacity and 25- gram weight, were formed by means of an extruding machine, bottles of excellent transparency were obtained very easily.

DMA an 2 g m of methy m h ryl .3 gram of a similar test was carried out with similar bottles produced Rongalite, and 1,500 cc. of distilled water were added, and the from only a olyvinyl chloride, in which case the average resulting mixture was agitated at high speed for 30 minutesresult was 2 drops for breakage. Thereafter, the charge was heated to 60 C. and caused to react for 5 hours.

To the latex thus obtained, 200 grams of methyl methacry- EXAMPLE 2 late containing gram of CHP gram of The process as set forth in Example I was followed except gram of RQngahter n 600 of dlsuued water were further that the degree of cross-linking was changed, and the methyl added: whlch was agitated for 30 mmutes- Thereafter, methacrylate to be added in the second step was added in the the batch was maintained at an elevated temperature of 60 C. l 5 fi Step Representative examples relating to the result-mg and caused to react for 5 hoursproducts are indicated in the accompanying Table i.

TABLE 1 Plastics constituent Rubber constituent Methyl- Methyli i DMA' i t mu: Butadiene Styrene DMA Styrene acry a e arcy a e 1 (parts by (parts by (parts by (parts by (parts by (parts by (parts by (parts by Sample weight) weight) Weight) welght) welght) weight) weight) weight) r ff 40 10 0. 25 0. 175 0 0 10 0. 15 10 0. 850 10 0. 3 10 0. 25 15 10 0. 600 10 0. 2 10 0. 25 15 10 0. 10 0. 1 10 0. 25 15 10 0. 15 10 0. 05

DMA: Triethylene-glycoldimetliacrylate.

The latex thus obtained was salted out at C. with a 1- 35 Number of Im act re eated Anti-stresspercent salt solut1on, further heat treated at C., and iii resistgnca drags (500 Trans. whitening tered. The powder particles filtered out were washed with rise cc., 25 g. parencyv through water and then dried, whereupon an MBS resin of v,,,/c value sample i p/ (p rcent)' bottle) percent bending of 0.032 was obtained with a yield of 98.5 percent. (Invention): d 2 "9.0 C 13 parts of this resin was mixed wlth 87 parts of a polyvinyl A E 3 5 1532m chloride of a polymerization degree of 800 containing 2 parts 13 '22 D0- of dibutyl-tin-dilaurate, and the resulting mixture was roll- I225 32: kneaded at C. for 4 minutes and then pressed at 190 C. under a pressure of I00 kg./cm. into a sheet of 3 mm. M80 10 9 670 Poor. thickness. 45 G 0.065 11 10 68.3 Do. H 0.040 11 0 72.2 Do. The Charpy impact strength of this sheet as tested on a I 0.035 12 8 76.4 Do- Charpy impact strength tests were carried out on notched test pieces of resins with varying blend proportions, and the point of transition from brittle fracture to ductile fracture was taken in each case.

TABLE 2 Rubber constituent, Plastics constituent, parts by weight Number of. Anti-stressparts by weight Impact repeated whitening Methyl- Methylresistance drops (500 Transproperty Buta- Sty- Stymethacmethacrise cc., 25 g. parency through Sample dicnc rcne DMA rene rylate DMA rylate DMA /c (percent) bottle) (percent) bending (A) 40 10 0. 25 15 20 0.175 0 0 0. 045 13 20 l 70 0 Good. J V 40 10 0. 25 15 15 0.176 5 0. 025 0. 032 12 22 1 80. 5 Exttiitiit. (E). 1 40 i0 0. 25 15 10 0.150 10 0. 05 0. 032 11 20 l 81. 5 Do. K. 40 10 0. 25 15 5 0.125 15 0. 075 0. 033 13 27 1 8i. 5 Do. It. 40 10 0 25 15 2 0.120 18 0.080 0.033 15 l5 1 81.0 D0.

DVB* DVB DVB 1 Glass clear.

*DVB: Divinyl-benzene.

50 parts by weight of the rubber constituent obtained in exactly same manner as set forth in Example 1 was graft- (Sample No. S), the impact resistance thereof deteriorates extremely.

What we claim is:

fi ggz t zf 22233 2 "9"; f a 5 l. A process for producing a graft copolymer of styrene and followinyTable 3 in am: e g m 3 methyl methacrylate upon a butadiene polymer compatible into am galfld added g: e i c with polyvinyl chloride, and for use in obtaining a polyvinyl e w r cons n two chloride resin composition having improved transparency, im- P? c s pact resistance, anti-stress-whitening through bending, which [he solution viscosity and physical properties of PVC comprises. shaped articles obtained in the same manner as in Example l a. re arm a latex of a butadlene l mer b ol menzln are shown n Table 3. p p g p0 y p y 8 TABLE 3 Rubber constituent, Plastics constituent, parts by weight Number of Anti-stressparts'by weight Impact repented whitening Methyl- Methylresistance drops (500 '[runsproperty Buta- Sty- Stymethacmethaerise 00., 25 1:. pnmncy through (bone rene DMA rene rylate DMA rylate DMA /c (percent) bottle) (port-nut) bonding 40 10 0.25 5 20 0.15 10 0. 05 0. 031 l2 l0 1 70. ll IIXGHIII'JIL. 40 10 0. 25 1O 16 0. 10 0.05 0. 032 l3 15 l 75. 0 D0. 40 10 0. 25 15 10 0.15 10 0. 05 0. 032 11 20 141.5 D0. 40 10 0. 20 5 0.15 10 0. 05 0.031 13 22 2 s0. 5 Good. 40 10 0. 25 2 O. 15 3 0. 05 0. 032 12 8 3 65. 0 Poor. l Strong yellow. 2 Glass clear. 3 Strong blue. I

Sanples N, O, and Q are presented for comparison purposes, in Vlihich and Q, indicates the case where the amount of MMA is extremely smal As seen from Table 3, above when the quantity of styrene in the rubber constituent is small (Sample Nos. N and O), the obtained article assumes strong yellow and possesses poor trans- N and 0 indicates the caes where the amount of styrene is extremely small,

a monomer selected from the group consisting of butadiene, and a mixture of butadiene as the principal constituent and styrene in the presence of a small quantity of parency. On the contrary, when the quantity of styrene is 30 a divinyl cross-linking agent, saidpolymer latex containlarge, the shaped product assumes strong blue, is non-trans- 8] from 40 to 75 Parts y weigh! of said bul-adlene arent, and poor in anti-stress-whitening through bending. in P X order therefore to obtain the shaped product satisfying the addmg to Sam latex from 60 to 25 pans y h of styrene and methyl methacrylate monomers in a ratio of desired propertles, the optimum blending rate of styrene and 80 parts by weight of styrene to 60-20 parts by weight methyl methacrylate 18 40-80 percent by weight of styrene d 6040 teem b Wei ht ofmeth lmethac late of methyl methacrylate and a small quantity of a dlVlllyl an pa y g y W cross-linking agent copolymerizable with said monomers,

EXAMPLE 5 1. said methylmethacrylate being divided into two por- I tions, from 10 to 90.percent by weight of which is 50 parts by welsht of rubber con-Sums! Obtained In exactly 0 added to the latex together with said 40 to 80 parts by Same manner as set forth in Example I was grail-polymerized weight of styrene in the first stage graft polymerization, with varying blend rate of styrene and methyl methacrylate and monomer mixture and resins respectively containing 80, 59, 2 h remainder portion f hi h i dd d i l to h and 38 percent of the rubber constituent were obtained as latex i h second stage graftoly erization, h 3 shown in Table 4 below. greater part of the first polymerization step is The solution viscosity and physical properties of' PVC m l d, shaped article obtained in accordance with Example lare 3. the quantity of said cross-linking agent being in the shown in Table 4. range of from 0.0l to 5 percent by weight of the total TABLE 4 Number Rubber constituent, Plastics constituent, parts by weight of re- Anti-stress parts by weight Impact peated whitening Methyl- Methyl- Rubber resistance drops (500 Trons property Buta- Sty- Stymethaemetham content rise 00.. 25 g. pnrcncy through Sample dienc rene DMA rene rylate DMA rylate DMA (percent) m /c (percent) bottle) (percent) bonding 40 10 0.25 5.5 35 0.054 3.5 0.0175 80 0.020 8 12 1 77.0 Poor. 40 10 0.25 15 10 0.15 10 0.05 0.032 11 29 81.5 Excellent. 40 10 0.25 35 23 0.35 23 0. 115 38 0.036 18 5 1 70.0 D0. 1 Slight yellow. 2 Glass clear. Samples R and S are presented for comparison purposes.

As seen from Table 4, above in case the rubber content is quantity of the monomers existing in the copolymer large (Sample No. R), a good result can be obtained when the and being present in each monomer portion; and shaped article is subjected to Charpy impact strength test, c. reacting the mixture to form said graft copolymer.

though the actual destruction resistance thereof is poor and its anti-stress-whitening property is also inferior. This is due to the fact that, as the rubber content in the resin thus obtained is high, the resin is prone to coagulate at the time of salting out, which prevent it from dispersing perfectly in the polyvinyl chloride. On the other hand, when the rubber content is small 2. The process according to claim 1, wherein the cross-linking agent is one selected from the group consisting of divinyl benzene, diethylene glycol dimethacrylate, triethylene glycol dimethacrylate, tetra-ethylene glycol dimethacrylate, and 1,3- butylene glycol dimethacrylate. 

2. the remainder portion of which is added singly to the latex in the second stage graft-polymerization, when a greater part of the first polymerization step is completed,
 2. The process according to claim 1, wherein the cross-linking agent is one selected from the group consisting of divinyl benzene, diethylene glycol dimethacrylate, triethylene glycol dimethacrylate, tetra-ethylene glycol dimethacrylate, and 1,3-butylene glycol dimethacrylate.
 3. the quantity of said cross-linking agent being in the range of from 0.01 to 5 percent by weight of the total quantity of the monomers existing in the copolymer and being present in each monomer portion; and c. reacting the mixture to form said graft copolymer. 